Precious metal alloy



June 13, 1933. E. M. WISE 1,913,423

PRECIOUS METAL ALLOY Filed Jan. 28, 1929 2 Sheets-Sheet 1 A .0 100/ k C 0 v 1o so I 6 10 so me 0 Ebwemtoz Kama/v0 M W/Jf 33a; 4. Gum w g M, Mau e.

June 13, 1933. E. M. wIsE PRECIOUS; METAL ALLOY Filed Jan. 28, 1929 2 Sheets-Shee't 2 AAAAAA 111 AVAVAVAYiZfiQY-MN vv a L v A Patented June 13, 1 9 33 UNITED STATES PATENT OFFICE" EDMUND M. WISE, OF J'ERSEY CITY, NEW JERSEY, ASSIGNOR TO THE INTERNATIONAD NICKEL COMPANY, INC., A CORPORATION OF DELAWARE PRECIOUS METAL ALLOY I Application filed January 28, 1929. Serial No. 335,481.

This invention relates to improved alloys of palladium, silver and copper, and to a novel method of heat-treating the same, and more particularl to alloys of the above metals having a l iigh tarnish and corrosion resistance, a high hardness value and other characteristics which render them especially suitable for dental use, and for other advantageous uses such as heat and electrical conductors.

One of the objects of the invention is to provide an improved metal alloy which is white in color, which is resistant to corrosion, and which is both strong and ductile.

Another object is to provide a metal alloy which is particularly adapted for dental, and electrical and heat conductive purposes.

Still. another object is to provide an alloy having a high resistance to tarnish, and one having a comparatively high hardness value and tensile strength.

The invention also consists in certain new and original features of construction and combinations of parts'hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompan ing drawings forming a part thereof, in w ich Fig. 1 is a ternary diagram showing the range in composition of an alloy of palladium, silver and copper in accordance with the present invention;

Fig. 2 is a ternary diagramshowing the composition of the alloys divided in accordance with tarnish resistance;

Fig. 3 is a ternary diagram range of hardenable alloys;

Fig. 4 is a ternary diagram showing the range of alloys which are particularly suitable for dental purposes; and

Fig. 5 is a graphic diagram showing the efiect of heat treatment at various temperatures on the hardness of certain alloys.

showing the In the following description and in the claims elements will be identified by specific names for convenience, but they are intended to be as generic in their application to similar elements as the art will permit.

In accordance with the present invention alloys consisting of palladium, silver and copper have been found to have a resistance to tarnish and corrosion which is dependent upon the relative percentages of the various metals and sometimes upon the heat treatment to which they are subjected. lying in the area A B C of the diagram of Fig. 2 have been found to be substantially completely resistant to both tarnish and cor- Alloys rosion. Alloys lying in the area D E B A of that diagram are largely resistant to tarnish and corrosion and may be-considered within a useful range, while the remaining alloys possess this property to a less degree.

The area A B C may be approximately represented analytically by stating that the palladium represents from 35% to 98% and is not less than 35+ (ti/7X Cu), the copper content being not lessthan 1% and the silver constituting the remainder of the alloy, but being not less than 1% of the total. The area .of useful alloys represented as D E C 0n the diagram may be defined analytically as containing from 25% to 98% palladium, the palladium content being not less than 25+ (4/11 X Cu), the copper being not less than 1% with the silver constituting substantially the remainder of the alloys, but being not less than 1%. The last equation relating to the minimum percentage of palladium required may be approximated by the following equation expressed in percent:

Palladium is more than the 1 quantity (22+ the percentage of copper).

The resistance to corrosion and tarnish 'represented by the curves of Fig. 2 was de-' termined by subjecting the alloys to moist H S vapor. The arrangement used consisted of a desiccator containin a solution of sulphuric acid in water (43 H SO by wt.) This solution will maintain 50% relative humidity in the desiccator. A small beaker containing a solution of sodium polysulphide was also placed in the bottom of the desiccator which maintains a small concentration of H S in the chamber. It should also be noted that the vapor also contains a trace of H 80 The samples prepared by polishing and rubbing with dry alumina were placed on a tray in the desiccator and allowed to remain fifteen hours or longer as indicated. The specimens were then removed and half of the specimen rubbed with alumina to remove any tarnish that might be present.

The amount of tarnish was then noted and utilized in the formation of the above mentioned diagram. This particular type of a tarnish test is employed because it is the one in common use in the dental trade and is the well known means for classifying alloys as to their tarnish resistance properties.

It has been found that certain allo 5 may, by suitable heat treatment, have the1r hardness and tensile strength materially increased. It has also been found that the heat conductivity and electrical conductivity of the hardenable alloys can be increased by a precipitation heat treatment. Referring to ig. 3, the allo s in which substantial hardening will take place upon heat treatment are represented by the area above the dotted line in that figure. It may be approximately represented analytically by stating that the palladium content varies between the limits of 25% and 62.6% with the copper percentage greater than 5+1.544 10- (Pd35) and less than 48%, with silver constituting substantially the remainder of the alloy. The solid curves representalloys that have been hardened to Rockwell B values of 80-110. The aforesaid equation showing the relation between the percentage of alladium and the percentage of copper may e expressed by an equation which is a simple approximation thereof. The approximating equation expressed in percent is as follows:

Palladium is less than the quantity (42+ the percentage of copper).

It will be understood that the temperatures for heat treatment may be varied within considerable limits. Desired results have been obtained by heating the alloys to a temperature in excess of 700 C. and then quenching in water. It was found that in this way the tensile strength and hardness were materially. decreased while the ductility was in creased, so that the quenched alloy could be cold rolled or drawn into wire or sheet form. An increase in tensile strength and hardness was obtained by heating this quenched alloy for a period of time varying from 15 minutes to an hour at a temperature of from about 350 or 400 to 500 or 550 C. and then allowing the alloy to cool slowly.

A considerable increase in tensile strength and hardness will result if after treating at 450 C. the alloy be quenched from this temperature, but the results obtained by slow cooling from that temperature were generally superior.

The increase in hardness on the Rockwell B scale is illustrated for two representative alloys in Fig. 5, the alloys having been previously treated at 860 and quenched and subsequently treated at the temperature indicated on the diagram for a period of aproximately 30 minutes and quenched. urve 6 shows the results of heat treatment of an alloy of 40% Pd, 45% Ag, 15% Cu. Curve 7 re resents an alloy of 40% Pd, 46% Ag, 10% u and 4% Ni. It is to be noted that for the alloys shown, a reheating temerature of 450 C. was found to produce the st results.

As an alternative heat treatment by which good results are obtained, the alloy ma be annealed at a temperature in excess of 00 C. and cooled from this temperature at a rate substantially slower than air cooling. The desired rate may be conveniently obtained by permitting the alloy to cool in silocel.

It has been found that an alloy having a composition of 3555% Pd, 55-5% Ag and the remainder Cu can be given a tensile strength in excess of 100,000 pounds per square inch by suitable heat treatment. As a specific instance, the influence of heat treatment on the tensile strength of an alloy containing substantially 40% palladium, 40% silver and 20% copper may be noted. The ultimate strength of this alloy after quenching from 860 C. was 97,400 lbs. per square inch. After aging for 30 minutes at 450 C. and quenching, the tensile strength increased to 149,000lbs. per square inch and after aging for 30 minutes at 450 C. and slow cooling, the tensile strength was increased to 171,000 lbs. per square inch.

For dental purposes it is very desirable to utilize an alloy which may be hardened to a certain degree and which will be largely resistant to tarnish and corrosion. A suitable range of alloys for this purpose is represented by the area within curve FGHI of Fig. 4. It is to be noted that this range is located in that area at which substantial hardness may be obtained, as shown in Fig. 3, and in which a high degree of tarnish and corrosion resistance is obtained, as shown in Fig. 2.

In addition to the above mentioned features, it has been found that the alloys described are all substantially white with practically a total absence of other colors. This white color renders these alloys especially suitable for dental purposes. Furthermore, when properly heat treated, they are of comparatively high electrical conductivity, which in connection with their non-corrosive properties, renders them most suitable for electrical contacts. The density of the alloys is relatively low and therefore their costs per unit volume is lower than that of man of the gold alloys which they replace.

Alloys in which palladium is present in amounts of less than 25% ossess a high heat and electrical conductivity and have a meltin point much higher than coppersil-v ver a1 oys containing no palladium. These alloys may be useful in cases where color and tarnish resistance are "of less importance. Alloys containing 30-90% Pd with copper I the principal remainder may be useful for electrical contacts. Two alloys which have. been found particularlyfsuitable for this purpose comprise Pd 80%, Cu 20% and Pd 58%. and Cu 42%.

In addition to the three elements, palladium, silver and copper, various other elements may be present in small amounts de ending upon the particular requirements 0 the alloy. For example, the soundness and denseness of the castings may be improved as for instance by the presence of a deoxidizer such as zinc, silicon oron, magnesium or calcium or compounds thereof. The deoxidizer should be a metal or metalloid such that the heat of formation of its oxide is substantially v in excess of the heat-of'formation ofcopper oxide, in order toinsure the complete deoxidation of the alloy. Calcium boride in an amount of a proximately .2 percent has been found suita 1e for this purpose.

Small amounts of other metals may be added to the above alloys without departinlgl from the spirit of the invention. Sma amounts of noble metals such as gold, platinum and rhodium may be resent and base metals such asnickel or co alt may be present up to about 4%.

-It is obvious that thecomposition of the above alloys and the temperatures employed in heat treatment may vary over a wide -range' Certain definite figures have been given by way of example only. Furthermore, the uses of the alloy are not limited to the few instances given. They may be em ployed in various arts wherein their particular charactertistics are of advantage.

In the initial heat treatin operation the alloy may be cooled as by air cooling from a high temperature, for example 860 C. and subsequently age hardenedas above described. The cooling in this case should be sufficient to prevent. the formation of substantial amounts of a compound composed of palladium and copper in the approximate ratio of their atomic weights. It has also been found that slow cooling of alloys within the hardenable range serves to increase their electrical conductivity. Alloys of 40% palladium and 5% to 20% copper, with the remainder silver are particularly suitable for this purpose and by slow cooling from a temperature in excess ing said allczy 0 v a proved product has been set forth and described and is pointed out in the claims, it is obvious that various changes may be made in the process or in the separate steps thereof without modifying or changin the essential features and characteristics 0 the product produced and that such product remalns substantially thesame although slight modifications may be made in its appearance, texture and in its physical and chemical character: istics. 1

,What is claimed is:

1. A method of increasing the electrical conductivity of a palladium, silver, cop er alloy comprising approximately 40% pa adium 5% to 20% copper and the remainder silver, which comprises heatin said alloy to .a temperature in excess of 00 C. and slowly cooling the same from this temperature.

2. A method of heat treating an allo of palladium, copper and silver composed of palladium from about 25% to 98%, copper i working, said alloy being substantially free from iron and analogous metals impairing the ductility thereof, which comprises heatto a temperature 1n excess of about 7 00 and below the meltin point of the aforesaid alloy and then quick y cooling the same.

3. A method of heat treating an alloy of palladium, copper and silver,v composed of not less than 10% and not more than 50% copper, 27% to 61% palladium, the percentage of palladium being more than (22 plus of the percentage of copper. present) and less than the quantity (42 plus of the percentage of copper present) and silver to an extent of not less than 1% and constituting substantially the balance, said alloy being substantially free from iron and analogous met als impairing the ductility thereof, which comprises heating the aforesaid alloy .to a

temperature in excess of about 700 C. and below the meltin point of the alloy, rapidly cooling or quenc ing the alloy, whereb the said alloy is rendered amenableto mec anical working and then reheating the alloy to a temperature of about 350 C. to about 550 C. for a sufficient period of time to harden the same. I.

- 4. A method of .heat treating an allo of palladium, copper and silver, composed of not less than 10% and not more than 50% copper, 27% to 61% palladium, the percentage of palladium being more than (22 plus of the percentage of copper present) and less than the quantlty (42 plus a of the percentage of copper present), andsilver to an extent of not less than 1% and constituting substantially the balance, said alloy being substantially free from iron and analogous metals impairing the ductility thereof, which comprises heating the aforesaid allo to a temperature in excess of about 700 and below the meltin point of the alloy, rapidly cooling or quenc iing the alloy, whereby the said alloy is rendered amenable to mechanical working and then reheating the alloy to a temperature of about 350 C. to about 550 C. for a sufiicient period of time and slowly cooling the reheated alloy to harden the same.

p 5. A method of heat treating an allo of palladium, copper and silver, composed of not less than 16% and not more than 50% copper, 30% to 61% palladium, the percentage of palladium being more than (22 plus of the percentage of copper present) and less than the quantity (42 plus of the percentage of copper present, and silver to an extent of not less than 1% and constituting substantially the balance, said alloy being substantially free from iron and analogous metals, impairing the ductility thereof, which comprises heating the aforesaid alloy 25 to a temperature in excess of about 700 C. and below the melting point of the alloy and then slowly cooling the thus heated alloy at a substantially slower rate than air cooling to harden and strengthen the said alloy.

6. A method of heat treating an alloy of palladium, copper and silver composed of from 25% to 62% of palladium, copper not less than 5% and not more than 48%, the copper content being as follows :not less than 5% for a palladium content of 25% to not lessv than 7 for a palladium content of-40% to 50%, not less than 15% for a palladium content of 50% to 55%, not less than 25% for a palladium content of 40 55% to 62% and silver not less than 1% and constituting substantially the balance, said alloy being substantially free from iron and analogous metals, impairing the ductility thereof the improvements of which comprises the heating of the alloy Within the range of 350 G. to 550 C. for a time sufficient to give a substantial increase in hardness and strength.

In testimony whereof, I have hereunto set my hand.

EDMUND M. WISE. 

